The invention relates to a pulsating electric field (PEF) treatment system for preserving fluid products by means of a pulsating electric field, comprising at least one electric supply source and at least one fluid flow path including at least one fluid treatment unit, which at least one fluid treatment unit comprises a fluid flow channel and at least two electrodes connected with the supply source for generating the pulsating electric field between the electrodes in the fluid flow channel, wherein the electrodes are included in the fluid flow channel and are each provided with a plurality of fluid flow through openings included in the fluid flow channel through which openings, in use, the fluid products flow.
The invention also relates to a treatment unit arranged for use in the system according to any one of the preceding claims, wherein the treatment unit comprises a fluid flow channel and at least two electrodes connected with the supply source for generating the pulsating electric field between the electrodes in the fluid flow channel, wherein the electrodes are included in the fluid flow channel and are each provided with a plurality of fluid flow-through openings included in the fluid flow channel, through which openings, in use, the fluid products flow.
Such a system and treatment unit is, inter alia, known from U.S. Pat. No. 3,933,606.
The preservation of food products is an important industrial and commercial activity which is mainly based on the inactivation or destruction of microorganisms in food products. The preservation of fluid food is initially based on the work of Louis Pasteur. In 1864 he developed a method for preventing extraordinary fermentation in wine by destroying the microorganisms responsible therefore by means of a heat treatment. To this day a heat treatment has been the most frequently used method for preserving fluid flood. The effect of the heat treatment on the quality of the end product depends on the duration and the temperature of the heat treatment. Apart from the fact that microorganisms are deactivated, the heat treatment also has negative side effects in a number of cases. In an attempt to minimize these negative side effects, the industry has concentrated, inter alia, on treatment of short duration at a high temperature. To date, however, attempts to use a heat treatment in which most of the microorganisms are deactivated without the occurrence of chemical or physical changes in the product have been unsuccessful.
In reaction thereto systems of the type defined in the opening paragraph have been developed. In these systems pulsating electric fields of very high intensity are generated in the fluid products to be preserved. The expectation was that the food subjected to such a treatment remains xe2x80x9cfreshxe2x80x9d and has a long shelf life. Besides, it appears that the method does not have the above-mentioned negative side effects.
According to the present insights it is a fact that in the pulsating electric field treatment system the activity of bacteria and other microorganisms is reduced because the cell structure of the bacteria and the microorganisms is damaged by the pulsating electric field. This electric field generates an electric potential over the membrane of a living cell. This electric potential causes an electric charge difference in the cell membrane. When this electric potential exceeds a specific threshold value, pores are formed in the cell membrane. When this threshold value is largely exceeded, more pores are formed, while, moreover, the thickness of the cell membrane decreases. This implies that the cell is destroyed.
In the known system according to U.S. Pat. No. 3,933,606 the electrodes each consist of a plate having a plurality of flow-through openings. This is therefore a system for a continuous treatment of fluid products.
A problem in the known apparatus is, however, that an undesirable inhomogeneous electric field and/or a disturbance of the fluid flow pattern occurs in the fluid flow channel. This has the result that the fluid product is irregularly treated. Besides, it appears that a relatively large energy supply to the electrodes is necessary for destroying the microorganisms. This implies, however, that during the treatment the temperatures of the product to be treated can rise to such a value that the above-mentioned negative effects begin to occur in a heat treatment. Moreover, it appears that only a small percentage of the microorganisms to be destroyed is actually destroyed. Another problem of the known apparatus is that this apparatus is not suitable for industrial use. One example of an industrial use is a flow rate exceeding 1,000 liters per hour.
Moreover, attempts to increase the effectiveness of the known treatment system by further increasing the intensity of the electric field involve the risk of electric breakdown. It is also possible that the originally neutral molecules are ionized and that the liquid begins to evaporate locally. It is an object of the invention to provide a solution for the above-mentioned problems.
The present invention provides a treatment system which applies a pulsating electric field to fluid products traveling along a fluid flow path. The system includes at least one electric supply source and at least one fluid treatment unit that has at least two electrodes connected with the supply source for generating a pulsed electric field between the electrodes in a fluid flow channel that is disposed in the fluid flow path. The invention is characterized in that the electrodes are each provided with a number of wires composed to form a net, with the fluid flow-through openings being formed between the wires of the net.
The specific design of the fluid treatment unit of the treatment system results in a homogeneous electric field being generated. Moreover, the homogeneous electric field has practically no influence on the flow pattern, so that the residence time distribution of the fluid products in the fluid treatment unit is uniform. It further appears that 30% less energy supply to the electrode is required than in the known system. This, in turn, has the result that the above-mentioned disadvantageous thermal effects do not occur. It is also possible that the system according to the invention is used with fluid flows exceeding 1,000 liters per hour. Since in the system according to the invention high electric field intensities are possible with an energy supply the amount of which is comparable to the amount of the energy supply of conventional systems, this implies that a higher percentage of the microorganisms to be deactivated is actually deactivated.
Preferably, the at least one treatment unit comprises a tube made of an insulating material, provided with a flow-in opening and a flow-out opening, the electrodes being included in the tube and the surface stretched by the net of each of the electrodes being directed at least substantially perpendicularly to an axial axis of the tube at the location of the relevant net.
The at least one treatment unit particularly comprises 2-20 electrodes spaces apart in the fluid flow direction. Between each pair of adjacent electrodes a pulsating electric field can be generated.
The system particularly comprises 1-20 treatment units included in the at least one fluid flow path. These treatment units are preferably connected in series.
The treatment unit suitable for use in the system according to the invention is characterized in that the electrodes are each provided with a number of wires composed to form a net, with the fluid flow-through openings being formed between the wires of the net.
FR-A-25 13 087 discloses a treatment system for treatment of fruit pulp wherein the electrode consists of a mesh. However, the fruit pulp flows in a direction perpendicular to the generated electric field between the electrodes.